Magnesium batteries have received significant attention as potential replacements for lithium batteries due to their high volumetric capacity, lack of dendrite formation, and the relative inexpensiveness of magnesium. Discovery and development of suitable electrolytes for magnesium batteries has proven challenging however. Conventional inorganic magnesium salts have typically been found incompatible with reversible magnesium deposition as they tend to form an ion-blocking layer at the magnesium electrode during their electrochemical reduction. On the other hand, organic magnesium salts such as those derived from Grignard reagents have been found to be highly corrosive, particularly toward non-noble cathodes, possibly due to the presence of chloride co-anions.
Previous studies have shown that magnesium borohydride and related magnesium boron cluster salts are effective as liquid electrolytes in magnesium batteries, possessing high compatibility with metal and the versatility to function with a variety of magnesium-compatible cathodes. In virtually all such systems studied to date, the electrolyte has been present as an ethereal solution, as ethers are the only solvents known to be compatible with magnesium.
The use of solid electrolytes generally has several advantages relative to comparable liquid electrolytes, including but not limited to a direct increase in energy density of the battery. A small number of solvent-free, or solid magnesium electrolytes have been reported. However, the known solid magnesium electrolytes generally have insufficient magnesium mobility to be practical in a magnesium battery at a desirable operating temperature.